Automatic power tool



1969 s. s. KIESTER ET AL 3,477,521

AUTOMATIC POWER TOOL 2 Shets-Sheet 1 Filed 001'.- 5, 1967 N V v 3% MW SRW INVENTORS GEORGE S. KIESTER R STANFORD SHORT v 777 ATTORNEYS Nov. 11,1969 cs. 5. KIESTER ET AL AUTOMATIC POWER TOOL v2 Sheets-Sheet 2 FiledOct. 5, 196'? INVE NTORS GEORGE S. KIESTER R STANFORD SHORT ATTORNEYSUnited States Patent US. Cl. 173-12 9 Claims ABSTRACT OF THE DISCLOSUREThe specification discloses a comparatively simple automatic power toolthat turns on by engagement with work to be driven, and which turns offupon a predetermined torque being attained. A novel clutch and powercontrol assembly is provided in which a driver element driven by themotor has a plurality of ca-m surfaces or grooves formed therein,preferably three, which receive radially movable drive transfer ballswhich coact with an axially slidable follower element as well as aslotted driven element. The halls coact with a conical cam surface endof the follower, the opposite end of which engages a clip which actuatesa sleeve mechanism containing a ball release assembly that operates tocontrol the air supply to the motor in response to the torque applied tothe implement portion of the tool.

This invention relates broadly to improvements in clutches andmechanisms controlling the supply and shut off or motive fluid to tools.More specifically, the invention is directed to clutch and on-otfassemblies which are adapted for use in portable power-driven tools usedfor setting screws, nuts, bolts, and the like. One embodiment shown asexemplary of the clutch and on-otf assembly of this invention is anautomatic screw driver particularly designed for driving screws or thelike into precision assembly components.

Heretofore such portable tools were equipped with a clutch mechanismincluding driving and driven members which have jaws axially movableinto or out of operative engagement. Another class of clutches of whichthis invention is one, employ intermediate drive transfer members, suchas ball bearings which move radially between a driving and drivenmember. These are the so-called rolling impulse clutches, examples ofwhich are found in US. Patents 2,263,709; 2,882,704; 2,957,323;2,964,151; and 2,986,052. The camming surfaces of a driver cam push thedrive transfer balls radially outward, and the driver is free to rotaterelative to the driven element. In a common form, vertices defined atthe juncture of adjacent surfaces of a polygonaldriver cam can passunder the balls. As the driver cam vertices rotate, a rolling force isimparted to the balls, hence the name rolling impulse clutch. Thisrolling disengagement of the balls permits release of the driven elementrelative to the driver when the resistance to rotation of the toolimplement reaches a predetermined maximum. In some of these examples,e.g. 2,263,709", the motor continues to operate although the driven toolimplement portion of the device ceases its rotary motion in response tothe frictional resistance imparted on it by the fastener that is beingdriven, and the ratchet like impacting sound signals the operator toremove the tool from the work.

In both 2,263,709 and 2,882,704, the clutch is used merely as anoverload release mechanism and there is no motor control means inconnection therewith. In US. Patents 2,957,323 and 3,005,325 such anoverload release mechanism is used in combination with an axiallymovable jaw clutch. In the former patent the motor continues to runalthough the bit no longer imparts rotation to the work. The repeatedimpacting created by the passage of the vertices of the driver camsurfaces under the driving balls forcing them radially inwardly andoutwardly is transmitted through the tool to the work as shock, andcontinued rotation wears the cam surfaces rapidly. The Patent 2,957,323represents an advance over 2,263,709 insofar as engagement with the workactuates means for turning on the tool motor, rather than turning onbeing entirely independent, but the turning off in both was notautomatic and must be operator controlled.

In both 2,964,151 and 2,986,052 there is provided automatic on and offactuating means in connection with a rolling impulse type clutch, butboth require complex lever type mechanisms that are not simple ofconstruction or maintenance. Further, the turning 01f of the motor isnot actuated until the moment of or after the release and impacting ofthe drive transfer elements.

OBJECTS Therefore, it is among the objects of this invention to providea self-starting power operated tool, which Will conserve the powersupply by operating only when the tool is applied to the work.

It is another object of this invention to provide a clutch and powercontrol assembly which actuates means for automatically stopping toolrotation upon the attainment of a predetermined torque by shutting offthe motor which actuates the tool, and which thereby increases tool lifesince the motor and clutch parts are not continuously in operation.

It is another object of this invention to provide an adjustable,presettable torque responsive clutch of the type in which radiallymoving balls engage a driven element but which are not radiallyreleasable from the driving element until after shut-off and therebyfunction to minimize wear of the clutch mechanism.

It is another object of this invention to provide a clutch assembly thatmay impart a single rolling impulse to drive transfer elements but onlyafter release at a predetermined torque.

It is another object to provide a clutch assembly having fewer drivetransfer elements which thus has less wear and is simpler and cheaper ofconstruction.

It is still another object to provide means for auto.- maticallystarting the motor of the tool as the operator applies the tool to thework with a minimum of force.

Other objects of our invention will appear from the detailed descriptionwhich follows.

IN THE DRAWINGS FIG. 1 is an enlarged longitudinal View partly insection through an automatic power tool embodying the clutch of ourinvention, and showing the parts in normal position just prior tosuflicient axial force being applied to the tool by engagement with thework tobe driven so that the motor commences to operate;

FIG. 2 is an enlarged longitudinal view partly in section through anautomatic power tool embodying the clutch of our invention showing theparts in position when the motor and tool implement portion are in theoperating position;

FIG. 3 is a vertical view partly in section on the line 3-3 of FIG. 2; 2

FIG. 4 is a vertical view partly in section on the line 4-4 of FIG. 2; 7

FIG. 5 is an enlarged longitudinal view partly in section through anautomatic power tool embodying the clutch of our invention and showingthe parts in a position just prior to shut-off when the torque ofdriving the; fastener has just reached a predetermined maximum va ue;

FIG. 6 is a vertical view partly in section on line 6-6 of FIG.

FIG. 7 is an enlarged longitudinal view partly in section through anautomatic power tool embodying the clutch of our invention and showingthe parts in the position when the torque from the driving of thefastener shuts oft the motor of the tool, the reversing valve being inthe position for reverse rotation operation.

SUMMARY The objects of our invention are achieved by providing a novelclutch in which a driver element driven by the motor has a plurality ofcam surfaces or grooves formed therein, preferably three, which receiveradially movable driven transfer balls which coact with an axiallyslidable follower element as well as an apertured, preferably slotted,driven element. The balls coact with a conical cam surface end of thefollower, the opposite end of which engages a clip which actuates asleeve mechanism that operates to control the air supply to the motor inresponse to the torque applied to the implement portion of the tool. Thedrive transfer elements are in continuous engagement with the driverwhile the motor is on, and in one embodiment may be retained fromtravelling radially a suflicient distance to completely disengage by alip portion of the follower element. Rolling impulse may be imparted tothe drive transfer balls only after the motor is turned ofi and as aresult of inertia, thus acting as a safety release. The details of themechanism are more easily seen by reference to the accompanyingdrawings, in which like symbols designate corresponding parts throughoutthe several views.

DETAILED DESCRIPTION Reference numeral 10 indicates a driven toolelement such as a screw driver bit for the work, such as a screw 12. Thebit 10 is removably held in a sleeve-like bit holder which is anextension of a driven element of a clutch spindle 55. The bit 10 has ahexagonal portion 36 received in a hexagon socket 37 of the bit holderto impart rotation to the bit when the holder is rotated. The bit isheld in the sleeve by means of a ball 32 in a slot 35 of the bit holder,the bit being provided with a groove 33 in the hexagon portion 36 forthe ball, the ball being biased into the groove by a C-shaped leafspring 34.

The bit 10 and the bit holder 20 are located within a housing 38 whichis threaded into a housing 40 containing reduction gears and a pneumaticmotor 74. Since the motor and gearing that may be used herein are of anyconventional type, e.g., such as that shown in US. Patent 3,289,715, adetailed description is unnecessary. A particularly useful motor andvalving assembly are shown and claimed in our co-pending applicationSerial No. 673,212 filed Oct. 5, 1967.

Within the forward end of the housing 38 (left hand end of FIG. 1) isslidably mounted a finder sleeve 41 backed by a spring 42 seated againsta flange in the housing 38. Appreciable axial movement is permitted bythe detent ball, slot, and spring retainer assembly 32, 35 and 34, andis needed to achieve the clutch function. A spacer 43 prevents the bitholder 20 from moving axially too far forward (to the left as seen inFIG. 1). Thrust applied to the working end of the bit 10 causes the bitto move axially, engaging and moving a thimble 44. A cross-piece stop 45limits the axial movement of the thimble 44 as best seen in FIG. 2. Thismovement of the thimble 44 in turn causes rearward movement of a spool47. A thimble ball 48 is confined in a hole 39 of the thimble 44 and isin contact with a camming surface 49 of a spool 47. Since the diameterof the ball 48 is larger than the annular thickness of the thimble 44,it will transfer axial movement to the spool 47 as long as it isradially outwardly confined. The spool 47 in turn moves a rod 50, a ball71, and an extension 70 to open the throttle valve assembly 51 (FIG. 2)and turn on the motor 74 in housing 40. With the thimble 44 in thisposition, the thimble ball 48 is moved closer to a counterbore 30 in thesleeve 52. The sleeve 52 is biased by a spring 53 to maintain contact ofits right hand end with a clip 54 axially slidable in slot 66 in driverspindle 55 (FIGS.2and 3).

Rotation of bit 10 by the spindle 55 and thereby rotation of the screw12 is achieved through the driving action of drive transfer balls 56seated in slots 57 in the spindle. As can be seen best in FIG. 4, threedrive transfer balls 56 coact with driver cam surfaces 58 formed on thedriver 46. The cam surfaces are in the relationship to each other assides of an equilateral triangle, but the ends of the cam surfaces donot meet to form apices. The three driving balls 56 are biased to seaton the triangular driver cam surfaces 58 by the attendant action of theconical cam surface 59 of follower sleeve 60 which in turn is biased bytorque adjustment follower spring 62. The biasing force of followerspring 62 is adjustably preset by altering the compression of thespring, through the use of threaded nut 63 which is held in the adjustedposition by lock washer 64.

The holes 57 in the spindle 55 may be round or, preferably, are in theform of a slot of arcuate length substantially greater than the diameterof a drive transfer ball 56. The arcuate slot permits rotational lostmotion of the balls 56 as the follower returns to normal positions.

Referring now to FIGS. 5 and 6, when the bit 10 encounters a sufiicientresir 'ance to rotation, the torque imparted thereto causes relativerotation of the driver 46 with respect to the spindle 55. The rotationcauses the driving balls 56 to be pushed radially outward by the drivercam surfaces 58. This radial movement of the driving balls 56 istranslated to forward axial movement of the follower sleeve 60 by theconical cam surface 59. Forward movement of the follower sleeve 60carries with it clip 54 which is axially retained within the followersleeve 60 against the shoulder 65, as best seen in FIGS. .2 and 5. Slot66 in spindle 55 permits of follower sleeve 60 with its retained clip 54to move axially relative to spindle 55 to contact and move sleeve 52 inan axially forward direction, as best seen by comparing FIGS. 2, 3 and5.

As best seen in FIG. 5, the movement of sleeve 52 against the sleevebias spring 53 brings the counter-bore portion 30 of the sleeve intoposition over the radial opening 39 in thimble 44 containing the ball48. Air pressure on the throttle valve assembly 51 is translated throughrod 50 to the spool 47 in a forward direction. This forward bias on thespool 47, by the action of cam surface 49, urges the ball 48 radiallyoutward in the hole 39 provided in thimble 44. When the counter-bore ofsleeve 52 passes sufficiently over the hole in thimble 44, the ball 48is forced completelyout of the groove in spool 47 so that the spool willpass axially forwardly under the ball 48. When the ball 48 releases thespool 47, the air pressure acting on throttle valve assembly 51overpowers the spool lbias spring 67thus permitting the throttle valveto close as in FIG. 7. When the throttle valve closes, motor 74 isimmediately shut off and the rotation of the bit 10 ceases. Due tospring bias of the follower spring 62, both the clip 54 and thefollower.

60 immediately return to their normal positions as illustrated in FIG.7. When the tool is removed from the work, that is, when the thrustagainst the bit 10 is released, the spool 47, thimble 44, ball 48 andsleeve 52 return to their normal positions shown in FIG. 1. In-thisnormal position, it will be noted that ball 48 will be received in spool47 ahead of its camming surface 49, and spring 53' will bias sleeve 52axially rearwardly so that the counter-bore portion 30 of the sleevewill be moved out of a position overlying the hole 39 in thimble 44.

The follower sleeve 60 may be so dimensioned that the drive transferballs 56 can ride over the driver tip 73, but the axial length of thefollower sleeve 60 and other parts are so. proportioned that thethrottle valve shutoff assembly 51 is normally actuated to turn off themotor before the override occurs. The override can occur due to theinertia of the tool bit parts but transmittal of torque reaction to theoperator is minimized. The shut-off response occurs before the ballspass over the vertices 73 and inertia alone causes the override. At lowinertia conditions the balls remain in constant contactwith the drivercam surfaces 58 while high energy conditions can and do result in theballs passing the vertices.

The throttle valve 51 is provided with a threaded shank portion 68 topermit adjustment and to compensate for tolerance and Wear variations inthe tool. The valve stem extension 70 is prevented from rotating by ball71 making the adjustment easily accomplished by inserting a screw driverthrough the air inlet 72 in head 69 and turning the valve by the slotprovided therein. The ball 71 located between the rod 50 and thethrottle valve extension 70 also serves to provide a close clearance fitcondition with the hole 75 through the rotor axis (FIG. 7). In thispreferred construction, air leakage into the clutch cavity is therebyrestricted.

No particular provision has been incorporated in the clutch assembly toinsure rotational freedom of the follower sleeve 60 relative to the clip54 which is prevented from rotation by the action of the depending prongagainst the sides of the slot 66 in spindle 55 (FIG. 3). In actualpractice, however, the follower sleeve 60 does rotate with the clutchaction, thus distributing wear from the action of the driving balls 56.This increases parts life and helps to maintain the accuracy of theclutch assembly.

The function of the shut oif assembly, and more particularly of clip 54and follower sleeve 60, can be achieved by alternate and equivalent partconfigurations or design. Within the spirit of the invention of theparticular configuration illustrated is preferred for manufacturingsimplicity.

The stop 45 is provided as a preferred construction to attain theoptimum accuracy in operation of the clutch assembly. It is apparentthat the end of the driver 46 could act as a stop means for the spool47. However, the position of the end of the driver during operation isaffected by the tolerance of many parts, and since not entirelypredictable is insutficiently reliable.

As best seen in FIGS. 1, 2 and 7, the triangular cam surfaces on thedriver are semicircular grooves shaped to be substantially interfittingwith the drive transfer balls 56, rather than flat surfaces extendingrearwardly to the forward axial end of the driver 46. By this provisionof semicircular grooves on the order of size of the diameter of thedriving balls, the service life of the driver cam surfaces 58 isincreased since the stress area contacting the drive balls is fargreater than a tangent flat surface contact. This groove constructionalso permits the driver to be made as a portion of a unitized clutchassembly construction.

As best seen in FIGS. 5 and 6, the optional lip 61 on follower sleeve60' prevents the driving balls 56 from leaving spindle 55 should inertiacause sleeve 60 to travel forward beyond expectations.

The driver cam surfaces can be greater or fewer in number than three, orcan intersect to form true triangular apices (in cross section),provided due consideration is given to achieve -a functional assembly.But is it important that the inner diameter of the bore forming thefollower lip 61 be more than the diameter of the driver 46 plus thediameter of two driving balls 56. Of course, it is also required thatthe axial length of the follower 60 be sufficient so that the clip 54actuates the sleeve 52 to release the thimble ball 48 causing throttlevalve 50 to close and shut off the motor before or upon the drivetransfer balls reaching lip 61, at a given predetermined setting of nut63.

Both uni-directional and reversible rotation construction can beutilized in this tool. It is preferred to utilize a reversibleconstruction, as shown in the figures. Reversibility is achieved becausethe symmetry of the cylinder and motor end plates permits air to bevalved to either side and exhausted from the other side by a reversingvalve in the head assembly 69. As seen in FIG. 7, when valve 80 ispushed down against its bias spring, the reverse porting is exposed forthe air to pass in the direction opposite to that of FIG. 6, thusrotating the motor in the opposite direction. Uni-directionalconstruction can be achieved by using a fixed plug to replace thereverse valve 80 and having fixed porting corresponding to that in FIG.6. Alternatively, appropriately designed end plates and headconstruction could be employed to alter the porting pattern so that onlya uni-directional rotation is imparted to the bit.

From the foregoing specification it is evident that we have provided acomparatively simple automatic tool that turns on by engagement withwork to be driven, and which turns off upon a predetermined. torquebeing attained. This is particularly desirable in connection with screwsor the like for precision assembly components where an accurate torquecontrol is necessary. Prior art devices utilizing rolling impulseclutches give rise to impacting when the vertices of the driver camsurfaces pass underneath the driving balls forcing them radiallyinwardly and outwardly in rapid oscillatory radial motion. This istransmitted through the tool to the work as shock. By the provision ofour cammed ball clutch actuating a motor shutofi linkage the shock thatdevelops from prior art impacting or ratcheting clutch jaws is entirelyeliminated. Since the motor is immediately shut off the attendantreduction in wear provides a tool with a lengthened life.

We claim:

1. An automatic on-off tool of the character disclosed comprising:

(a) means for rotating a driver,

(b) a driver, one portion of which has a camming surface formed thereon,

(c) a directly driven rotatable tool holder disposed externally coaxialto said driver, one end of which receives said camming surface portionof said driver, said end having means for receiving a drive transferelement therein,

(d) a drive transfer element disposed in said receiving means of saidtool holder in contact with said driver camming surface,

(e) a generally tubular follower disposed exteriorly coaxially of saidreceiver end of said tool holder, said follower having a conical cammingsurface disposed to contact said drive transfer element,

(f) a throttle valve assembly,

(g) means for moving said throttle valve assembly, from an open positionto a closed position, in contact with said follower, which includes:

(i) means for effecting movement of said throttle valve to an openposition in response to force of application of said tool to awork-piece to be driven,

said opening means being releasably engageable with said throttle valve,and includes:

(a) first means in responsive contact with said tool holder, said firstmeans having a radially disposed aperture therein for receiving a ball,and

(b) second means in contact with said throttle valve and having a ballreceiving surface thereon, said second. means being disposed coaxiallyand received within said first means,

(c) a ball disposed in said aperture of said first means for contactwith said receiving surface of said second means,

7 (ii) means for releasing said opening means from engagement with saidthrottle valve in response to axial movement of said follower, saidreleasing means being disposed coaxially and exteriorly around saidfirst and said second means, and said releasing means includes arelieved portion therein, said second means and said releasing means arespring biased against said throttle valve and said followerrespectively, said relieved portion of said releasing means providingspace for movement of said ball when positioned over said aperture insaid first means in response to predetermined axial movement of saidfollower, thereby to release said second means in response to motivefluid pressure on said throttle valve to close said valve, whereby saidmeans for rotating said driver element is shut off when the torquedeveloped in turning said tool holder exceeds a predetermined value.

2. A tool as in claim 1, wherein said drive transfer element is a ball,and said camming surface is in axial cross-section a portion of a circlewhose diameter is slightly greater than said drive transfer ball.

3. A tool as in claim 1 wherein said driver has three camming surfacesformed thereon, said surfaces lying in a common plane perpendicular tothe axis of said driver, and the ends of said surfaces are spaced fromeach other along the exterior surface of said driver.

4. A tool as in claim 3 wherein said drive transfer element is a ball,and said camming surface is in axial crosssection a portion of a circlesubstantially interfitting with said drive transfer ball.

5. A tool as in claim 1 wherein said follower includes a retaining lipportion formed as a continuation of the outermost periphery of saidconical camming surface substantially parallel to the axis of saidfollower, thereby to retain said drive transfer elements in continuousradial contact with said driver cam surfaces.

6. A tool as in claim 5 wherein the inner diameter of a bore in saidfollower forming said lip is less than the diameter of said driver plusthe diameter of two drive transfer elements.

7. A tool as in claim 1 wherein said drive transfer element is a balland said means for receiving a drive transfer element in said toolholder end is a slot having an arcuate length substantially greater thanthe diameter of a drive transfer ball.

8. A tool as in claim 7 wherein said driver has three camrning surfacesformed thereon, said surfaces lying in a common plane perpendicular tothe axis of said driver, and the ends of said surfaces are spaced fromeach other along the exterior surface of said driver.

9. A tool as in claim 8 wherein each of said camming surfaces are incross section a portion of a circle substantially interfitting with adrive transfer ball.

References Cited UNITED STATES PATENTS 2,694,151 12/1960 Eckman l73-l2X3,205,992 9/1965 Clapp 192 3,288,258 11/1966 Taylor 192 150 3,289,71512/1966 DeGroff etal 19215OX ERNEST R. PURSER, Primary Examiner

